In ink-jet printing methods, droplets of ink are directly projected onto a recording medium from very fine nozzles and allowed to adhere to the recording medium, to form images or characters. The ink-jet printing methods have become rapidly spread because of various advantages such as easiness of full coloration, low cost, capability of using a plain paper as the recording medium, non-contact with printed images or characters, etc.
In recent years, in order to impart a good weathering resistance and a good water resistance to printed matters, an ink containing a pigment as a colorant has been extensively used.
On the other hand, there is an increasing demand for commercial printed matters printed on recording media using a low-liquid absorbing coated paper such as an offset-coated paper, or a non-liquid absorbing resin film such as a polyvinyl chloride resin film, a polypropylene resin film and a polyester resin film.
It is known that when images or characters are printed on the low-liquid absorbing or non-liquid absorbing recording media by the ink-jet printing methods, there tends to occur problems such as slow absorption of liquid components, prolonged drying time owing to poor absorption, and deterioration in rub fastness early after printing. Also, it is known that unlike a plain paper in which a pigment is likely to be penetrated, the low-liquid absorbing or non-liquid absorbing recording media tend to suffer from deposition of pigment particles remaining thereon which are directly susceptible to an external force, so that the images or characters printed on these recording media tend to be deteriorated in rub fastness even after being dried.
In order to solve these conventional problems, ink-jet printing methods using recording media having an ink-absorbing layer have been proposed.
For example, JP 2008-260279A discloses an ink-jet printing method using a recording medium having a pigment-containing coating layer in which an amount of pure water transferred to a surface of the recording medium on which the coating layer is provided, and a pH value of the same surface of the recording medium are controlled to respective specific ranges, and images or characters are printed on such a surface of the recording medium using an ink containing a granular coloring material, an emulsion resin and a surfactant and having a pH value of 8 or more. In addition, JP 2008-260279A proposes a recording apparatus equipped with a drying device.
However, the improvement in recording medium and recording apparatus tends to have problems concerning costs, consumed powder, etc., and therefore it is desirable to improve the composition of inks.
JP 2005-36202A discloses an ink-jet printing method using a water-based ink containing colorant-containing water-insoluble vinyl polymer particles and a void-type glossy medium in which the water-insoluble vinyl polymer is produced from a polyoxyethylene chain-containing (meth)acrylate monomer, a salt-forming group-containing monomer and a hydrophobic monomer.
JP 2008-101192A discloses an ink-jet printing method in which an ink constituted of a solid component containing a colorant and a resin and a liquid component having a boiling point higher than that of water is ejected to print images on a recording medium, and a ratio between the solid component and the liquid component as well as the viscosity of the ink are respectively controlled to specific ranges.
JP 2003-105234A discloses a water-based ink for ink-jet printing which includes a salt-forming group-containing polymer A, a salt-forming group-containing polymer B and/or a salt-forming group-free polymer C in which the amount of a salt-forming group per unit weight of the polymer B is smaller than that per unit weight of the polymer A.